The present invention relates to a method for operating an internal combustion engine, which has a secondary air line system for introducing secondary air into the exhaust system and to an internal combustion engine having a secondary air line system for introducing secondary air into the exhaust system.
Secondary air injection systems are used for decreasing hydrocarbon (HC) and carbon monoxide (CO) emissions during the cold start of internal combustion engines. Fresh air is blown onto the exhaust gas side using this system, and thus HC and CO are afterburned. Simultaneously, the exhaust gas temperature increases, and the catalytic converter reaches its effective operating temperature sooner.
A secondary air injection system of this general type is known, for example, from U.S. Pat. No. 6,094,909 (=WO 97/38212). The basic construction may be seen from FIG. 2. The secondary air is taken through a line 13 from the filtered air side of the intake system of the internal combustion engine upstream of a throttle valve 33 and pumped through a compressor 26 via a line 14 into the exhaust area 31. Various valves may be used to control the system. The compressor 26 may be driven by a turbine 35, corresponding to FIG. 3, which makes use of the partial vacuum produced in the intake manifold through the throttle valve 33. However, the pressure differential in the intake manifold before and after the throttle valve required for driving the turbine only arises in operating states with a closed or nearly closed throttle valve. The application known in the prior art is in gasoline engines.
The soot-laden particles in diesel motors have recently been filtered via diesel particulate filters. These diesel particulate filters become loaded with soot to a maximum permissible back pressure within hours and must then be regenerated. This regeneration is typically performed by combusting the accumulated soot. The required temperature for burning off the soot particles is preferably provided via supplemental auxiliary systems. In general, one differentiates here between continuously (passively) and discontinuously (actively) operating systems as well as corresponding combinations of both types. Active systems include diesel particulate filters having burner regeneration or having thermoelectric regeneration. Regeneration systems having fuel burners require sufficient combustion air in addition to the fuel supply. The systems with thermoelectric regeneration also require combustion air for completely burning off the soot particles.